The present invention relates to safety equipment used on machinery for processing plates, etc., such as presses and shearing machines, where physical injury of the operator is prevented by controlling the machinery for safety purposes if any part of the operator's body approaches the danger zone of the machinery and to a safety tester for checking whether or not the said safety equipment on the machinery for processing plates, etc., works satisfactorily.
When machinery for processing plates, etc., such as presses and shearing machines operates with great power, it is well known that the operator faces the danger of receiving a serious injury as part of his body such as the hands and fingers might be caught by the machinery if the operator operates the machinery in error.
In order to prevent such danger, various inventions (devices) have been presented to date, but these devices have the defect of being unsatisfactory in confining the operator's free activities. For instance, in a mechanical safety device, a netting is provided covering the danger zone so as to allow only the material to pass for processing. In this case, however, the safety equipment netting must be changed every time the processing material is changed. Moreover, although the operator appears to be safe as he is separated from the machine by the safety device, attention should be paid to the fact that it is safer to keep the space between the machine and the operator as free as possible. On the other hand, in an optical safety device, the danger zone of the machine is illuminated and a photoelectric switch works to stop the machine when the operator's hand enters the illuminated zone. In this case, however, it is impossible to distinguish the operator's hand from the material in process and the safety device may often work unnecessarily. Moreover, it may also operate because of light sources external to the safety device. On account of these defects, it is of low reliability and not very satisfactory as a safety device.